1. General introduction 17 1. A. B. C. Figure 4. Illustration of an electronically-controlled pneumatic jet injector-assisted treatment with bleomycin and lidocaine in a keloid scar. (A) Before administering treatment, the electronically-controlled pneumatic jet injector (EPI) hand piece with the injector tip is placed perpendicularly on the keloid scar. (B) A crosssectioned illustration of the injector tip and nozzle of an EPI-device. The liquid container within the EPI contains a solution with the combination of bleomycin and lidocaine (depicted in blue). (C) Illustration during injection. The EPI device generates a high-velocity jet stream that punctures the epidermis of the keloid, disperses the combination of bleomycin and lidocaine in the mid-deep dermis and creates visible skin papule or blanching. Recently, also the first needle-free jet-injector that relies on laser energy, the Mirajet, was commercialized.43 This EPI uses an Erbium YAG laser that generates vapor bubbles to generate pressure. These NFIs are yet being used to deliver small volumes in the superficial layers of the skin,27 and therefore they are probably more appropriate for soft tissue rather than treatment of keloids or other rigid skin disorders. Currently, a smaller and more affordable NFI prototype is being developed for medical applications by the group of Prof. Fernandez Rivas from the University of Twente. These NFIs operate using lasers with microfluidic components. Up to date this prototype has been investigated in skin models such as porcine skin. Potentially, in the future these NFIs may be used as portable device in a home setting by patients for indications such as acne scars and alopecia areata. The choice of jet injector may depend on the treatment indication, because the penetration depth and distribution patterns vary among jet injectors (Table 1). Other 0.5 mm
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